( 1)rt⊿abc,rt⊿bcd,rt⊿cda,rt⊿dab,rt⊿aob,rt⊿boc,rt⊿cod,rt⊿doa.

(2) If CF is connected, ∠ ECF = 90, CE = CF, ∠ CFG = 45.

∠FCG=∠HCG-∠HCF=90 -∠HCF

∠ECH=∠ECF-∠HCF=90 -∠HCF

∴∠FCG=∠ECH

∠∠e = 45 ,∴∠e=∠cfg，

∴⊿FCG≌⊿ECH (corner)

∴ CG = CH, ⊿ CGH is an isosceles right triangle.

(3) The area of quadrilateral CGFH is equal to the sum of the areas of ⊿FCG and ⊿FCH,

∵⊿FCG≌⊿ECH (corner kick), ∴ fg = eh, fg+FH = eh+FH = ef.

If FG and FH are regarded as the bottoms of ⊿FCG and ⊿FCH, then the height is the distance from point C to EF, and the distance from point C to DF is 4.

s⊿fcg+s⊿fch= 1/2fg*4+ 1/2fh*4=2(fg+fh)=2ef

EF=2*4=8

The area of quadrilateral CGFH =2EF=2*8= 16.